Rand Paul’s chief strategist is leaving his Senate post to run the Kentucky Republican’s political shop.

Doug Stafford, who is widely seen as Paul’s closest adviser, will soon resign as chief of staff to manage Paul’s national political operation. Today’s news is the clearest sign yet that Paul, a potential 2016 contender, is building a presidential campaign.

“It’s part of a natural evolution for Rand’s team,” says Trygve Olson, a Republican consultant who works with Paul. “Rand is doing a lot of things right now, so there’s a need to expand. Given Doug’s background in both establishment politics and grassroots politics, he’s a perfect fit.”

Stafford, a longtime conservative activist, first rose to prominence as Paul’s confidant during the 2010 campaign, and has been his highest-ranking Senate aide ever since. Previously, he was in the inner circle of Ron Paul’s presidential campaign, and worked as a consultant for the Campaign for Liberty.

Stafford will be focused on directing the senator’s organization in early-primary states, his calendar, and his communications. He will also run Paul’s political-action committees, which are expected to grow. Those groups — RAND PAC and Rand Paul for U.S. Senate — are the financial and political foundation for Paul’s likely presidential campaign.